Methods for mechanical computation are well-known in the prior art. (Svoboda, “Computing Mechanisms and Linkages,” New York, Dover Publications, 1965; Bradley, “Mechanical Computing in Microelectromechanical Systems (MEMS),” AIR FORCE INSTITUTE OF TECHNOLOGY, AFIT/GE/ENG/03-04, Ohio, 2003; Sharma, Ram et al., “Mechanical Logic Devices and Circuits,” 14th National Conference on Machines and Mechanisms (NaCoMM-09), 2009) However, while the earliest example of a Turing-complete design is probably Babbage's Analytical Engine, which was described in 1837 (although never built), the vast majority of previous proposals for mechanical computing are not Turing-complete systems. Rather, they are either special-purpose devices not intended to address general-purpose computing at all, or they are partial systems or mechanisms, lacking crucial capabilities which would allow them to provide Turing-complete systems. For example, with respect to partial systems or mechanisms, known examples include logic gates built from custom parts, kits, or even toys like Lego. Note that mechanical logic gates alone, even universal ones, do not by themselves permit Turing-complete computing; some memory means is also required. Turing-complete computing requires a means for combinatorial logic, as well as a means for sequential logic.
The mechanical computing literature also includes molecular-scale implementations of various computational components (again, often not Turing-complete systems), including (Drexler, “Nanosystems: Molecular Machinery, Manufacturing, and Computation,” New York, John Wiley & Sons, 1992; Hall, “Nanocomputers and Reversible Logic,” Nanotechnology, 1994; Heinrich, Lutz et al., “Molecule Cascades,” Science, 2002; Remon, Ferreira et al., “Reversible molecular logic: a photophysical example of a Feynman gate,” Chemphyschem, 12, 2009; Orbach, Remade et al., “Logic reversibility and thermodynamic irreversibility demonstrated by DNAzyme-based Toffoli and Fredkin logic gates,” PNAS, 52, 2012; Roy, Sethi et al., “All-Optical Reversible Logic Gates with Optically Controlled Bacteriorhodopsin Protein-Coated Microresonators,” Advances in Optical Technologies, 2012).
While previous designs for mechanical computing vary greatly, previous proposals capable of Turing-complete computing (as opposed to limited-purpose devices) tend to reply upon a substantial number of basic parts (or “primitives”) including various types of gears, linear motion shafts and bearings, springs (or other energy-storing means, e.g., some designs use rubber bands), detents, ratchets and pawls, or other mechanisms which have the potential to be energy-dissipative, as well as increasing the complexity of the device. Note that such designs require these various primitives to function properly; they are not optional.
That the use of many types of basic parts in a mechanical system can complicate design, manufacture, and assembly, as well as potentially reducing reliability, is obvious. Reducing the complexity of mechanisms is a common inventive goal.
Note also that many of the mechanisms used in previous proposals for mechanical computing generate substantial friction. Removing such mechanisms would have benefits beyond reducing device complexity, including reduced energy expenditure. However, judged by the prevalence of friction-generating mechanisms in mechanical computing systems, it is difficult to design around this issue.
Perhaps less evident than friction are other modes of energy dissipation, including vibrations, which may, e.g., create heat, or generate acoustic radiation. For example, ratchets and pawls, detents, or other mechanisms which involve the relatively uncontrolled impact of one piece of a mechanism upon another can lead to energy-dissipating vibrations, and so the removal of these types of mechanisms would also have benefit.
Waste heat is a well-known issue for computational systems, electronic or mechanical, which dissipate far more energy per bit operation than is required in theory. In theory, computations can be performed where the energy dissipated is only ln(2) kBT per irreversible bit operation. This is called the Landauer Limit (Landauer, “Irreversibility and Heat Generation in the Computing Process,” IBM Journal of Research and Development, 1961) and has been confirmed experimentally (Berut, Arakelyan et al., “Experimental verification of Landauer's principle linking information and thermodynamics,” Nature, 7388, Nature Publishing Group, 2012).
Note that the Landauer Limit only applies to irreversible operations. Reversible operations can, in theory, dissipate zero energy. While conventional computers are generally not built upon reversible hardware, reversible computing has been studied for decades (Landauer, “Irreversibility and Heat Generation in the Computing Process,” IBM Journal of Research and Development, 1961; Bennett, “The Thermodynamics Of Computation,” International Journal of Theoretical Physics, 12, 1973; “Logical reversibility of computation,” IBM Journal of Research and Development, 6, 1973; Toffoli, “Technical Report MIT/LCS/TM-151-Reversible Computing,” Automata, Languages and Programming, Seventh Colloquium, Noordwijkerhout, Netherlands, Springer Verlag, 1980; Toffoli and Fredkin, “Conservative Computing,” International Jounral of Theoretical Physics, 3/4, 1982; Bennett and Landauer, “The Fundamental Physical Limits of Computation,” Scientific American, 1985; Feynman, “Quantum Mechanical Computers,” Foundations of Physics, 6, 1986). For a general overview of reversible computing from a software perspective, see (Perumalla, “Introduction to Reversible Computing,” CRC Press, 2014).
Whether reversible or irreversible, novel designs for mechanical computational systems that have the potential to reduce device complexity (along with the associated design, manufacturing and assembly costs) and use less energy per bit operation than existing designs, would be quite useful. Not being subject to the Landauer Limit, reversible designs have the potential to ultimately use the least energy. However, existing computing systems use energy so far in excess of the Landauer Limit that even irreversible designs could greatly improve upon the state of the art.